Up to now, the III-V compounds, such as GaAs, having larger bandgaps than that of Si, are used for fabricating Schottky devices. Such Schottky structures having larger bandgaps and carrier mobilities are often applied in high-speed devices.
In a Schottky device manufacturing process, the Schottky barrier is greatly influenced by the surface state, surface oxidation, and concentration of background impurities. The reverse leakage current is also determined by the factors as mentioned above. Therefore, many researchers has made efforts to solve the above-described problem by developing a manufacturing method or a structure of the Schottky diode with a higher SBH and a low reverse leakage current.
It has been found that the surface state, impurities, and the instability of the semiconductor device (shown in Table 1) would influence the Schottky-barrier height. This is set forth in the article to the Metal Semiconductor Contacts, written by Rhoderick and Williams, and Moriarty's paper (Appl. Phys. Lett. Vol. 67 (3), p383-385 (1995)).
TABLE 1 ______________________________________ Bond Dissociation Energy .DELTA.H.sup.0 (kcal/mol) ______________________________________ Name of Semiconductor InSb -7.4 InAs -13.8 InP -18 GaAs -19.5 Name of Oxide Pr.sub.2 O.sub.3 -436 Al.sub.2 O.sub.3 -400 SiO.sub.2 -217.6 In.sub.2 O.sub.2 -221.3 Ga.sub.2 O.sub.3 -258.5 As.sub.2 O.sub.3 -156.1 As.sub.2 O.sub.5 -218.5 SbO.sub.2 -108.5 Sb.sub.2 O.sub.3 -169.4 ______________________________________
FIG. 1 shows a conventional Schottky diode structure. The conventional manufacturing method is to form a sulfide layer 102 over the substrate 101 by sulfuration and then to form a metal layer 103 over the sulfide layer 102 for increasing the SBH. It is found that the sulfuration can avoid the surface oxidation. However, sulfur has a weak atomic bonding ability with various III--V compounds (as shown in Table 2). Sulfur will evaporate from the surface of the device at a higher temperature such that the surface of the semiconductor device will be oxidized resulting in a reduced SBH.
TABLE 2 ______________________________________ Bond Dissociation Energy .DELTA.H.sup.0 Name of Compound (kcal/mol) ______________________________________ Pr.sub.3 S.sub.4 -371.5 Ag.sub.2 S -7.3 InS -32 In.sub.2 S.sub.3 -85 In.sub.5 S.sub.6 -185 GaS -50 Ga.sub.2 S.sub.3 -122.8 Ag.sub.2 S -7.3 AuS no NiS -22.5 Ni.sub.2 S.sub.3 -51.6 PtS.sub.2 -19.86 ______________________________________